1. Technical Field
The present invention relates to a technology of ejecting a liquid from an ejection nozzle.
2. Related Art
A liquid ejection apparatus which ejects a liquid, such as ink, using an ejection nozzle is widely known. Although a number of methods exist for ejecting a liquid from an ejection nozzle, as a typical example, a method is widely used whereby a piezoelectric element mounted on an ejection nozzle acts as an actuator, causing a droplet-like liquid to be ejected from the ejection nozzle by applying a predetermined voltage waveform to the piezoelectric element. Using this method, by changing the voltage waveform applied, it is possible to change the size of a droplet or a liquid ejection amount.
The piezoelectric element, as it is a capacitive load, has the property that, when a voltage is applied to the piezoelectric element, an electric charge is accumulated in the piezoelectric element and a voltage equivalent to the amount of electric charge accumulated appears as an applied voltage between the terminals of the piezoelectric element. For this reason, an electric charge has to be supplied to the piezoelectric element in order to increase the applied voltage, while an electric charge must be emitted from the piezoelectric element in order to decrease the applied voltage.
In order to drive the capacitive load at a high power efficiency, the following kind of technology is proposed. Firstly, a plurality of capacitors are charged by differing voltages. When increasing the applied voltage, an electric charge is supplied to the load by individually switching the capacitors to be connected to the capacitive load to higher voltage capacitors. When decreasing the applied voltage, by individually switching the capacitors to lower voltage capacitors, the electric charge of the capacitive load is recovered by the capacitors. By so doing, it is possible, when increasing the applied voltage again, to supply the capacitive load again with the electric charge recovered by the capacitors when decreasing the applied voltage, and increase the applied voltage, meaning that it is possible to drive the capacitive load at a high efficiency (JP-A-2003-285441).
However, in a case in which the piezoelectric element mounted on the ejection nozzle of the liquid ejection apparatus is driven by applying the technology of JP-A-2003-285441, there is a problem in that it is difficult to adjust the ejection amount of a liquid ejected from the ejection nozzle. That is, because the liquid ejection amount is based on the drive amount of the piezoelectric element, the ejection amount depends heavily on the maximum voltage or minimum voltage of a voltage waveform to be applied, but either a maximum voltage or minimum voltage is applied by connecting a capacitor which has been previously charged by the applied voltage to the piezoelectric element. Consequently, the voltage of the capacitor has to be changed in order to change the maximum voltage or minimum voltage of the voltage waveform. However, in the event that the voltage of the capacitor has been changed, when attempting to apply another voltage waveform, the maximum voltage and minimum voltage of the other voltage waveform also changes.
Of course, it is ideal that the voltage of the capacitor is changed for every voltage waveform, but as the capacitor is set to a large capacitance so that a stable voltage waveform can be output, it is not easy to change the voltage of the capacitor in the short time in which a voltage waveform switches. It is also conceivable, rather than using all the capacitors, to leave out, for example, a maximum voltage capacitor or a minimum voltage capacitor, and to connect the maximum voltage capacitor or minimum voltage capacitor to the piezoelectric element only when applying a higher voltage or a lower voltage, but with this configuration, the maximum voltage or minimum voltage of a voltage waveform fluctuates greatly, and the liquid ejection amount cannot be adjusted finely.